Positive influenza tests surged in Maine last week as reported flu cases reached their highest levels since the H1N1 flu outbreak during the 2009-10 season, according to state data released Wednesday.

While Maine and the New England states are seeing fewer cases per capita than much of the country, Maine has so far reported 682 positive flu tests, with 230 cases during the week ending Jan. 3 alone, according to the Maine Center for Disease Control. An additional 157 cases were reported during the last full week of 2014.

Nationally, the flu has hit hard in most of the country this season with 21 deaths recorded nationwide — none in Maine — and nearly 3,500 people hospitalized, according to the U.S. Centers for Disease Control and Prevention.

In Maine, there did not appear to be any significant outbreaks, such as schools closing or nursing home quarantines, although Central Maine Medical Center in Lewiston diverted patients to other hospitals for two hours Monday evening because they had too many people with influenza or flu-like symptoms, officials reported.

Maine Medical Center in Portland and MaineGeneral Medical Center in Augusta reported typical numbers of flu hospitalizations for this time of year.

In Brunswick, the Thornton Oaks Retirement Community curtailed some of its group activities because they had one confirmed case of the flu and a few others staying at home with flu-like symptoms. But officials there said the moves were mostly preventive.

During the 2009-10 flu season, the Maine CDC reported 1,060 cases, but in the four years since then cases topped out at less than 500 before this season arrived. Because flu season is unpredictable, and cases can peak at various times, it’s impossible to predict whether this season’s total will approach or surpass 2009-10, infectious disease experts say.

“Anything goes in the world of virology,” said Gwen Rogers, Maine Medical Center’s director of infection prevention.

Dr. Sheila Pinette, Maine CDC director, said one factor may be that the flu vaccine developed for this season is less effective than in previous years.

Unlike other vaccines, the flu vaccine is not always effective against all strains of the flu from season to season, as scientists try to predict what strain will be circulating, according to the U.S. CDC. This year, the vaccine did not closely match one of the most widely circulated strains, the agency says.

However, Pinette said it’s still important to be inoculated because the vaccine will work against three of the four strains. Also, the U.S. CDC points out that people who receive the vaccine but contract the flu tend to have less severe symptoms than those who forgo vaccines.

Pinette said the holiday season brings people closer together, and the cold weather keeps people inside more frequently, which also may be contributing to the sudden spike in flu cases.

At Thornton Oaks, Don Kniseley, the community’s executive director, said the facility hosts a vaccination clinic and closely monitors situations to make sure illness doesn’t spread.

“We try to be very proactive. Nearly everyone gets their flu shots,” said Kniseley, who expects that group activities will resume in the next couple of days.

At the Portland Community Health Center, no cases have been reported, and the center is aggressive at vaccinating most people who come through the door, as well as hosting two vaccination clinics, Dr. Alison Gorman said.

“We always have a real big push to get as many as we possibly can vaccinated,” Gorman said. The clinic serves many low-income patients and the immigrant population.

Rogers, at MaineMed, said the statewide increase may only be an increase on paper and not an accurate reflection of the actual number of flu cases.

She said it may be that the number of flu cases this season is typical, but that there’s increased reporting of the flu because more patients are requesting to be tested.

“Typically, once flu is established in an area, doctors stop testing for it,” said Rogers, explaining that flu is likely far more prevalent than the reported numbers, not only because some doctors stop testing, but also because some people with the flu never see a doctor and simply stay home until their symptoms subside and they recover.

She said more patients may be requesting flu tests because they want to obtain a prescription for Tamiflu, a drug that eases flu symptoms.

Rogers believes people are much more aware of the availability of drugs for flu treatment than they were a few years ago.

Joe Lawlor — 791-6376

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Twitter: @joelawlorph